1. Field of the Invention
The present invention relates to a control mechanism for a rotary disk of a dual-color injection molding machine, more particularly one, with which the rotary disk can rotate smoothly, and slow down gradually, and won't stop abruptly at an end of a rotation, helping increase efficiency of the molding machine.
2. Brief Description of the Prior Art
Referring to FIG. 8, a conventional injection molding machine 2, which is used for single-color injection molding, includes a bed, a fixed mold support 21 secured on the bed, a movable mold support 22, and an actuating mechanism 24 joined to the movable mold support 22. First and second half parts of a mold 23 are secured on the mold supports 21, and 22 respectively, and the actuating mechanism 24 moves the movable mold support 22 towards the fixed mold support 21 to join the half parts of the mold 23 together.
Referring to FIGS. 9 to 11, another conventional injection molding machine 3, which is used for dual-color injection molding, includes a bed, a fixed mold support 21 secured on the bed, a movable support 22, an actuating mechanism 24 joined to the movable mold support 22, a gear 33 rotary on the movable support 22, a rotary disk 31 joined to the gear 33, and a power source 32. First and second half parts of a mold 23 are fitted on the fixed mold support 21, and the rotary disk 31 respectively, and the actuating mechanism 24 is used for moving the movable support 22 towards the fixed mold support 21 to join the half parts of the mold 23 together. The power source 32 is used for causing angular displacement of the rotary disk 31 for allowing injection of a second color material into the mold 23. The power source 32 includes one or two manual directional select valves 34, several limiting valves 35, and left and right hydraulic cylinders 323, 324 connected to the valves 34, 35. Power output rods of the hydraulic cylinders 323, 324 are respectively connected to left and right racks 321, 322, and toothed sides of the racks 321, 322 face each other, and engage the gear 33. Thus, referring to FIG. 12, both the rotary disk 31 and the second half mold part will turn clockwise when the right cylinder 324 is actuated to project down at the power output rod thereof, and the left cylinder 323 is made to release oil. And, both the rotary disk 31 and the second half mold part will turn counterclockwise when the left cylinder 323 is actuated to project down at the power output rod thereof, and the right cylinder 324 is made to release oil.
However, the power source 32 is found to have disadvantages as followings:    1. The rotary disk 31 is likely to begin and stop movement abruptly, and the second half mold part can't move smoothly if the manual directional select valves 34 are not skillfully operated because the hydraulic cylinders 323, 324 will provide relatively large power for rotating the rotary disk and the second half mold part, and have relatively large diameter.    2. To stop an active one of the hydraulic cylinders 323, 324 at an end of an angular displacement of the rotary disk 31, the operator first has to make oil passages with smaller diameters connected to the active hydraulic cylinder instead of the original oil passages with the help of the manual directional select valves 34 as well as the limiting valves 35 such that speed of the power output rod is reduced, and then has to make oil passages with still smaller diameters connected to the active hydraulic cylinder instead such that the power output rod moves at still lower speed. And, after the above active cylinder stops, the other one of the hydraulic cylinders is actuated for make the rotary disk 31 rotate in the opposite direction. Therefore, the procedure for operating the power source 32 is complicated, and the power source is inefficient, and the rotary disk 31, and the second half mold part will stop movement abruptly, pause many times, and can't move smoothly when the valves 34 are switched; movement of the rotary disk 31, and the second half mold part can be presented with a trapezoid, which means there are pauses.    3. There will be much increase to the instant high pressure in the oil passages because the hydraulic cylinders 323, 324 are controlled in respect of speed, starting, and stoppage by means of changing the flow of hydraulic oil. Consequently, there will be higher rate of breakdown.